This invention relates to a process for the preparation of a tertiary perester by contacting an acyl compound with a tertiary hydroperoxide.
Tertiary peresters are commercially important initiators for the polymerization of monomers in particular, to acrylics, polyethylene, polyvinylchloride, and styrenics. Tertiary peresters are also used for the modification of these and other polymers. For the various methods of synthesis of peresters we refer to D. Swern, Ed., Organic Peroxides, Volumes I and II, 1970 and 1971, respectively, Wiley-Interscience, New York. On a commercial scale, tertiary peresters are prepared from tertiary hydroperoxides and acid chlorides in particular. This process has the disadvantage that acid chlorides are expensive starting materials. A further drawback is that the use of acid chlorides leads to the formation of hydrogen chloride, which is a corrosive. Also, the use of acid chlorides presents a problem in the form of chloride waste. Accordingly, there is a need for improved methods of preparing tertiary peresters.
Incidentally, Baba et al., Agric. Biol. Chem. 52 (1988) 2685-2687 describe the occurrence of enzymatic synthesis of hydroperoxides in the course of an enzymatic resolution of racemic secondary hydroperoxides in organic solvent by reaction with isopropenyl acetate in the presence of a lipoprotein lipase from Pseudomonas fluorescens (LPL Amano P). In this way, one enantiomer is acylated while the other enantiomer remains in the reaction mixture as the hydroperoxide. Acylated primary and secondary hydroperoxides are said to disintegrate spontaneously to carboxylic acid and aldehyde or ketone, respectively. More importantly, it is mentioned that no acylation reaction occurred starting from 1-methyl-1-phenylpropyl hydroperoxide.
Hoft et al. in Tetrahedron: Asymmetry 5 (1995) 603-608 also describe that 1-methyl-1-phenylpropyl hydroperoxide and 1-cyclohexyl-1-phenylethyl hydro-peroxide are not converted into the corresponding tertiary peresters using the same lipase.
Further, several publications describe the enzyme-catalyzed synthesis of peracids. In PCT Patent Publication No. WO 91/04333, for example, a process for preparing peroxycarboxylic acids from a carboxylic acid and hydrogen peroxide using an enzyme catalyst is described. The preparation of tertiary peresters is not disclosed in these publications.